Structure and activity studies of tyrosinases and related proteins

The copper-containing enzyme tyrosinase catalyzes the conversion of tyrosine into DOPAquinone, which is the precursor of melanin in almost all organisms. In humans, melanin is an essential pigment that protects the skin and eyes against the UV radiation from the sun. Mutations in the genes of the melanin biosynthetic pathway cause oculocutaneous albinism, a group of autosomal recessive disorders characterized by reduced or absent production of melanin in the skin, hair and eyes. In this thesis, we investigated the structure and activity of tyrosinases and related proteins, including human tyrosinase (TYR), human tyrosinase related protein 1 (TYRP1), and mushroom tyrosinase-associated lectin-like protein (MtaL). TYR and TYRP1 are membrane-bound glycoproteins that occur in melanosomes. Using a baculovirus expression system in insect cells we succeeded in producing large amounts of the intramelanosomal domains of TYR and TYRP1, allowing their crystallization. Elucidation of the crystal structure of TYRP1 showed that TYRP1 contains zinc ions in its active site, in contrast to TYR which contains copper ions. This explains why TYRP1 does not have tyrosinase activity. The structure of TYRP1 is the first structure of a mammalian tyrosinase-like protein. Therefore, the TYRP1 structure makes it now possible to give detailed explanations of various albinism-causing mutations. In addition, the TYRP1 structure provides a solid base for the design of highly-desired compounds for pigmentation disorder treatments that reduce melanin production. Analysis of the MtaL structure suggests that the protein may have a carbohydrate-binding site allowing the protein to bind to a glycoreceptor.